Electrochemical device for chemical analysis



United States PatentiO ELECTROCHEMICAL DEVICE FOR CHEMICAL ANALYSISLeland C. Clark, Jr., Yellow Springs, Ohio Application March 21, 1956,Serial No. 573,029

14 Claims. (Cl. 204-195) This invention relates to an electrolyticdevice for use in chemical analysis, and particularly to a polarographiccell adaptable for use in making quantitative analyses,

a polarographic cell and comparing that effect with known ordeterminable standards. In its simplest form the polarographic cellcomprises an anode and a cathode -in electrical circuit with each otherthrough a suitable -electrolyte or electrolyte forming substance. Theelectrolyte is provided by a compound, solution, or other suitablematerial which will form with the anode and cathode an electric cell,and which will provide ions for reactions with the substance which it isdesired to meas- =ure in such a way as to afiect the electricalcharacteristics of the cell.

The application of polarography to many fields of science has beenheretofore limited by the difiiculties encountered in undesiredreactions between the cell components which destroy the usefulness oraccuracy of the p cell, for example, by altering the properties of theelectrolyte so that the reaction between the ions and a certainsubstance in a composition under analysis is interfered with or notaccurately observable. Also, in some cases the cathode may become platedwith certain substances in the composition, thereby rendering the cellinoperable. As an example of such limitations in use 'of certainpolarographic cells, the measurement of free oxygen in certain gases hasbeen accomplished by bub- "bl'ing the gas through a liquid electrolytein which an anode and cathode are immersed. Such a method however is notfeasible with certain gases and with oils which are non-miscible withthe electrolyte used. Furthermore, it is necessary to standardize thecell under such circumstances and it is quite likely that in the proctobe analyzed could change the entire quantitative (or Sub- "evenqualitative) make-up of the composition and thus v the subsequentdeterminations would be erroneous as to the original composition.

In accordance with this invention the anode and cath- 'o de pair areelectrically connected through a captive" electrolyte or electrolyteforming substance which is protected from turbulence and preferably isphysically isolated and electrically insulated from the composition tobe analyzed by a barrier means permeable to the sub- ;stancewhiehitisdesired to measure, in..the composition, 5 electrolytematerial- 32, "preferably including a suitable 2,913,386 Patented. Nov.17, 1959 and which barrier means is impermeable to all otherconstituents of the composition which might have an efiect on theelectrical characteristics of the cell.

Accordingly, the primary object of this invention is to provide anelectrode pair supported in predetermined spaced relationship andelectrically connected by an electrolyte or a substance reactable toform an electrolyte, and to provide a selectively permeable barrier forseparating the electrode pair and the electrolyte or other substancefrom the composition to be analyzed.

A further object of this invention is to provide a cell for use inpolarography embodying a pair of electrodes supported in predeterminedspaced relationship and having a chamber around the electrodescontaining an electrolyte in sufficient quantity to provide anelectrical connection between them, and to provide a selectivelypermeable barrier means in a wall of the chamber for admitting onlydesired substances into the chamber for reaction with the electrolyte.

Another object of the invention is to provide such a cell includingmeans for adding a buffer solution to the electrolyte in accordance withthe need of such buffer to maintain the concentration of certain ions inthe electrolyte as desired.

It is an additional object of this invention to provide analyticalapparatus including a polarographic cell having an anode and a cathodeimmersed in an electrolyte and also having a membrane selectivelypermeable to the substance to be measured for isolating the cell membersfrom the composition to be analyzed, and including .suitable electricalcontrols and instruments for observing the quantity of electricalcurrent passing through the cell.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawing and the appended claims.

In the drawing- Fig. l is a detail view, partly in section and partly inelevation, of a cell according to the present invention;

Fig. 2 is a schematic diagram of a simple circuit in which the cell ofFig. 1 may be used;

Fig. 3 is a diagram of a circuit including the cell of .Fig. l and atype of galvanometer for use in observing the changes in conductivity ofthe cell over a wide range 0f values; and

Fig. 4 is a detail view of a modified cell.

Referring to the drawing, which illustrates a preferred embodiment ofthe present invention, and particularly .to Fig. 1, a typical cell inaccordance with the present invention is illustrated as including atubular body 10 defining a chamber closed at its upper end by a cap 12and having an insulating rod 15 supported coaxially therewithin by meansof an upper washer-like spacer 16, and a lower ring type of spacer 18slotted at 19 to provide passage for liquid to the lower end of thecell. Within the lower end of rod 15 there is a button-type cathode 20of a suitable conductive material connected to a cathode lead-in wire 22which extends within rod 15 to the upper end thereof. The lower outersurface 25 of rod 15 is coated with a suitable conductive mate rial 26to provide an anode, and an anode lead wire 27 extends through the upperspacer 16 and is wrapped around the lower or coated surface 25 of rod 15and suitably fixed thereto at a connection 28.

' The spacing between the anode and cathode, provided by the thicknessof the annular portion 29 of the lower end of rod 15, is thus maintainedin predetermined fixed relation, and the space directly below thisannular end portion 29 acts as-a 'bridge through which ions aretransferred and electrical current travels while the reactions occur inthe space directly below cathode 20. An

bufier, is suppliedto the well surrounding the lower end of rod "15 andthus "to the aforementioned "bridge and reaction spaces. This wellmaintains an adequate supply of electrolyte and assures an adequatesupply of ions at the appropriate electrode, as necessary for operationof the polarographic cell. Ifadditional solution is required after anextended periodof operation,such solution may be added as desiredthroughan opening intheside wall of tube 10, normally closed by a stopper 33.

"The electrolyte, the electrodes, and the bridge" and reaction spacesare-all isolated and electrically insulated from the outside of the tubeby a selectively permeable barrier -means provided by a membrane '35extending across theend of =tube 10 and ='heldinplace'by an O-ring seal36- rece'ive'd within the lower cap 38, which in turn is provided --witha relatively large central opening 40 to admit 'the composition to beanalyzed to the outer surface of membrane 35. The required spacingbetween membrane '35 and cathode 20 and the surrounding rod lower end 29can be provided by toughening the annular lower 'fiaceof the rod end2910 provide for access of the electrolyte to the cathode.

The material of which membrane '35 is formed varies in accordance withthe properties-of the gas, solution, or other composition which it isdesired to analyze. For example, when the-cell is-to be used fordeterminingthe oxygen contentof a gas or a solution, membrane 35 may beof polyethylene which will pass the oxygen to the interior of the cell,while forming a'barrier to other substances which would afiect theelectrical characteristics of the cell.

In "the operation of the cell the electrolyte 32 provides for the how ofelectrons -in the electro-reduction and electro-oxidation processes usedin polarography. In the determination of oxygen content, for example,these processes take place in accordance with the overall equationwherein H+ represents 'aI'hydrogen-ion, represents :an oxygen atom, ande represents an electron. Of course, for continual determination asuitable supply of ions must be provided, for continual combination orreaction with the substance being measured. :In determinations ofoxygen, as an example, regulation of .thehydrogen ion concentration tomaintain an adequate ;supply of such ions at the cathode may beaccomplished by adding a suitable buffer to the-electrolyte.

The sensitivity of the cell may also be affected to some degree byliberation of ionsfrom the noblemetal cathode at lowpotentials and,withelectrolytes of certain pH values. This sensitivity'can be overcome.to'a great extent by selecting cathodes having desirably high values ofovervoltage for the ions in :question. For example, it has been foundthat in a cell jforquse .in determinations of oxygen a gold cathodeextends the usefulness of the cell over awiderrangeof:pHvalues,:sincethegold has ahigh value of hydrogenoveryoltage.

The electrical characteristics of the cell will rbe'afiected inproportion to the quantity -of the substance :to be measured passingthrough membrane 35. :For instance, when measuring-oxygen the electricalcurrent carrying capacity of the cell will=vary-in-direct proportion tothe quantity of oxygen :passing into theelectrolyte, since :a sufiicientsupply of hydrogen ions will be maintained'by the butter -,in.theelectrolyte tending to polarize the cell, and the cell will bedepolarizedin proportionto oxygen reacting with the hydrogenions.

When suchacell is connected toa circuit :asin Fig. 2, so that an appliedvoltage of about' 0. 6 voltismainta'ined across ,thecell, a currentwillfiowiuthe presence of'the substance being measured since thatsubstance willtend to depolarize the cell. -Forexample,-current readingson thegalvanometer 45 will be proportional'tooxygen passing through theprotective membrane. .Such a..c e.ll,- havjngasiluer silverchlorideanode :andgaplatinumrcatllode in an electrolyte of an aqueous sodiumchloride solution, and suitably calibrated in gases having known oxygentensions, will give a current flow which is proportional to the quantityof oxygen contained in the composition being examined.

A simple circuit such as in Fig. 2 includes a battery 46 having apotentiometer 47 connected to the terminals thereof, and a voltmeter 48connected -between-the variable arm of the potentiometer and thepositive terminal of the battery. The potentiometer and voltmeterprovide for anaccurate adjustment of the potential difference desiredacross the cell, usually in the vicinity of 0.6 v. The cathode isconnected to the potentiometer contact on the negativeside of battery 46and the anode is connected to the positive terminal, with thegalvanometer 45 in the line to the cathode. Variations in the currentthrough the'cell, as observed on galvanometeri45,'will be in proportionto the quantity ofthe substance being-measured .passing through theselectively permeable 'jbarrier membrane 35 and reacting withions .inthecell-to alter its electrical characteristics.

vFig. 3 illustrates another circuit in which the cell of Fig. 1 may beused, for observing'relatively small electrical currents passing.through the galvanometer. In this :circuita battery 50 isconnected'through switch 52-.with a potentiometer 53. .A voltmeter 55.is connected between the variable arm of potentiometer 53 :and :the

negative terminal of battery '50, for the purpose of observing thepotential difference between the arm :of cthe potentiometerand thenegative battery terminal, vaud'thus to provide adjustment of the,desired voltage to beirnpressed across the cell. The anode is connected-to the potentiometer arm, and ;the cathodeis connectedtoihe centralterminal of a single pole double throw switch '56 movable between anupper maintain position at-contact57, and a lower fread position atcontact-58.

The galvanometer .60 is provided with a .plurality of shunting resistorsR1, R2 and R3 'in series with each .nection with the read contact 58.Switches 64 -and'62 are operated simultaneously'toselectdiiferent-seriesiand paralleled combinations of resistances in,circuit with'the galvanometer. For example, in the position shown R4isin series with the entire group of R1, R2 and .R3, which are in shuntwith the galvanometer.

The maintain contact 57 is connected to a third switch 65 connected at66 to operate with switches 62 and 64, and movable between threepositions .Wherein the cell is placed in series with one of .resistanccsR6 R7, or R8. The value of these resistances is selected so as tocorrespond to the total resistance of the ga'lvanometer and its variousshunt and series circuits in the three positions of switches 62 and 64and hence to balance the current and to maintainthe same resistanceregardless of whether .the switch 56 is in the read or the maintainposition. .Inpractice, the various resistances havebeen selected to givearange of galvanometer readings sensitive ;to variations of onemicroampereptwo microamperes and four microamperes witha battery ofone-half volt and with a potential difference acrossthe cell of about0.6 v.

It is also possible under certain circumstances to select electrodepairs'having a batteryactiomthereby providing mined potentialdifferenceacross-the cell are eliminated :and 1the :cell .lea'd wires connecteddirectly to agalvanometer or, other suitable device for observing and/orrecording the changes in current carrying capacity of such aself-energized cell. A cell of' this type is especially suited for usein situations where it is desired to have a continuous analysis of acomposition; but where a minimum of equipment requiring minimumattentionis also desirable.

It may also be desirable in some instances 'to utilizea non-electrolytictype of captive electrolyte substance in thec ell which will not conductunless combined with or subjected to certain substances, radicals, ions,and the like under study. Accordingly, the term electrolyte formingsubstance as used herein is intended to embrace those substances whichare in themselves electrolytes and also other substances which arecapable of reacting with other substances or radicals or ions understudy to form an electrolyte. For example, in studying the concentrationof certain ions in a solution, a normally non-conductive solution orpaste may be provided between the electrodes of the cell of suchcharacter that it will be reactable with such ions to form a conductingsolution or paste. 'Such a cell would then be standardized with knownquantities of ions under study, and used to test such ions with thepermeable barrier means selected to be permeable to such ions andimpermeable to others which fmightreact with the electrolyte formngsubstance to form an electrically conductive product.

It'will be appreciated that different types of apparatus may be used toobserve the electrical activity of the cell. For example, a recordinggalvanometer has been used'in a circuit similar to'the one shown in Fig.3 to providea continuous record of the changes in current flowingthrough the polarographic cell, and thus to give a continuous record ofthe quantity of the substance being measured. Successful results havebeen obtained with a cell utilizing a platinum cathode and asilver-silver chloride anode, and using an aqueous sodium chloridesolution as an electrolyte. This cell is utilized for the determinationof oxygen, and accordingly membrane 35 is formed from polyethylene.Suitable results have also been obtained in oxygen determinations usingas an electrolyte an aqueous solution of sodium chloride with addedglyceriner Other materials which have been found suitable for membrane35 in oxygen determinations are silas tic, rubber, and vinyl chloride.

7 It is also possible to provide a barrier means permeable only to thedesired substances by passing a thin film of selectively permeable fluidbetween two thin fixed permeable plates or membranes. Such a modifiedconstruction is shown in Fig. 4, wherein suitable membrane plates 70 and71 are supported in spaced relation, and a quantity of selectivelypermeable fluid, such as silicone oil, is passed between these platesfrom an inlet 74 to an outlet'75. Such a modified barrier meansfunctions in the same manner and for the same purpose as the membrane 35shown in Fig. 1.

;The-'pol'arographic cell provided by this invention is adaptable tomanyuses and to a variety of scientific and industrial fields. For example,the cell can be used to determine oxygen in a liquid, a gas, or a solid.A cell can be devised for use in determining such electro-reducible orelectro-oxidizable gases as S0 or to determine inert gases such as CO.In the latter instance, it may be desirable to have the inert gas reactwith special cell electrolytes whose electrical activity is affected inan irreversible way by the inert gas, and in such a case alarge'reservoir of the electrolyte solution can be maintained fordiffusion slowing in front of the electrode surfaces; In determiningsolids, or salts in solution, the per- 'meable barrier means is selectedso as to be permeable to certain ions. For example, certain membranesmade from ion exchange resins may be used, having surfaces structedinaccordance with this invention in small sizes such that the diameterofcap 38 is about one-half inch and the length of the cell is in the orderof four to five inches. Such a small cell can be calibrated in knownatmospheres and subsequently utilized as an altimeter, or used in a facemask for an aircraft pilot to provide a hypoxia warning device. Otherexemplary uses of the oxygen measuring cells are in determining thebasal metabolism of a patient by measuring the oxygen consumption bydifference between inspired and expired air and the volume of airexchanged, and in many industrial applications wherein it isdesired toknow the oxygen content of water, saline, sewage, oil, or othercompositions.

While the forms of apparatus herein described constitute preferredembodiments of'the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. A polarographic cell for use in analyzing a composition to determinethe quantity of a certain substance in said composition, said cellcomprising: an anode and acathode; means supporting said anode and saidcathode in fixed spaced relationship; means for confining an electrolyteforming substance in velectricalcurrent carrying contact with said anodeand said cathode; means for impressing a predetermined electricalpotential across said anode and said cathode; barrier means surroundingsaid anode and said cathode and said electrolyte forming substanceto'physically separate and electrically insulate said electrolyte fromsaid composition being analyzed, said barrier means being-permeable tothe substance'in said composition the quantity of which it is desired todetermine, said substance being reactable with said electrolyte formingsubstance to alter the electrical characteristics of said'cell, saidbarrier means being impermeable to all other constituents ofsaid-composition reactable with said electrolyte forming substance; andmeans for observing variations in the electrical characteristics of thecell caused by reactions between said electrolyte forming substance agilsaid substance to which said barrier means is permea e. I

2. In a device for use in determining the proportional quantity of asubstance in a composition of matter, the combination of: a pair ofelectrodes; insulating means supporting said electrodes in predeterminedspaced relationship; means defining a chamber around said electrodes; anelectrolyte contained in said chamber in sufiicient quantity to fill thespace between said electrodes; a membrane selectively permeable to thesubstance to be measured, said membrane forming 'one of the walls ofsaid chamber and being adapted to be exposed to the compositionofmatter, said membrane separating said electrolyte from saidcomposition and permitting passage of said substance therethrough intosaid electrolyte within said chamber; means for impressing apredetermined electrical potential across said electrodes; and means formeasuringthe current in the circuit comprising said electrodes andelectrolyte.

3. In an electrode assembly for exposure to a constituent to be measuredby polarographic analysis, the combination of: a first electrodeproviding a first surface thereon; a membrane selectively permeable tosaid constituent; means supporting said membrane with one face thereofclosely adjacent to said first surface to define a liquid film spacetherebetween, the'other face of said membrane being expo'sable to 'anenvironment containing said constituent to be" measured; a reservoir foran electrolyte; liquid passage means between said reservoir and saidfilm space for maintaining a film of electrolyte in said space; and asecond electrode positioned on the same side of said membrane as saidfirst electrode for contact with said electrolyte for forming anelectrical circuit between said firstmlebt-rode, said electrolyte, andsaid second electrode.

4. In an electrode assembly for exposure to a constituent to be measuredby polarographic analysis, the combination of a first electrodeproviding a first surface thereon; a membrane selectively permeable tosaid con stituent; means supporting saidmembrane with one face thereofclosely adjacent to said first surface to define a liquid film spacetherebetween, the other face of said membrane being exposable to anenvironment containing said constituent to be measured; a reservoir foran electrolyte forming substance, the volume of the reservoir beinglarge relative to the volume of said film space; a restricted passagebetween said reservoir and said film space for maintaining a film ofelectrolyte forming substance in said space; and a second electrodepositioned on the same side of said membrane as said first electrode forcontact with said electrolyte forming substance for forming anelectrical circuit between saidfirst electrode, said electrolyte formingsubstance and said second electrode.

5. In an electrode assembly for exposure to a constituent to bemeasured, the combination of: an electrically insulating support body; afirst electrode embedded in said support body and having an exposedsurface at a face of said body and substantially flush therewith;membrane means selectively permeable to" said constituent; means forsupporting said membrane with one face thereof closely adjacent to saidelectrode surface and said body face defining a liquid film spacebetween said membrane and said electrode surface and defining an ionicpassage between said membrane and said body face, the other face of saidmembrane being exposable to an environment containing said constituent;reservoir means for enclosing a body of electrolyte forming substance ofrelatively large volume compared with the volume of said film space,said reservoir means adjoining and communicating with said passage tomaintain a film of said electrolyte forming substance in said filmspace; and a second electrode positioned on the same side of saidmembrane as said first electrode for contact with said electrolyteforming substance for forming an electrical circuit between said firstelectrode, said electrolyte forming substance and said second electrode.

6. In a probe assembly for polarographic measurement of oxygen in agaseous or liquid medium, the combination of: an anode; a cathode; achamber enclosing-said anode and said cathode and adapted to contain anelectrolyte for bridging said anode and said cathode, said chamberincluding an oxygen permeable barrier forming a wall thereof; means formaintaining said barrier closely adjacent to said cathode to form anelectrolyte film space therebetween, said chamber isolating said mediumfrom access to said film space and said cathode except by way of saidbarrier; circuit means for applying a potential to said cathode and saidanode; and means coupled to said circuit means for indicating a currentin said circuit means as a function of oxygen permeating said membraneinto said film space.

7L In a measuring cell for determining'the presence of a particularsubstance in a composition of matter, the combination of: a chamberhaving an opening therein for communication with the composition ofmatter; an anode electrode and a cathode electrode; means for mountingsaid electrodes in said chamber in spaced relationship; selectivelypermeable and electrolyte forming means for blocking said opening andisolating said electrodes from the composition and forming an electriccurrent path between said electrodes; and means coupled tosaidelectrodes for impressing a predetermined electrical potentialacross said electrodesand-observing variations in the electrical currentcharacteristics of the cell as a function of the quantity of theparticular substance permeating into said chamber.

8. In a measuring cell,'the combination of: an anode electrode and acathode electrode; means for supporting said electrodes in saidcellinpredetermined spaced relationship; amedium electrolytically bridgingsaid electrodes to form an electrical circuit therewith; a chamberhaving two permeable walls permitting passage of selected substancesinto said chamber through one of said walls and out of said chamberthrough the other of said walls, the outer face of said one wall beingpositioned' to be exposed to a composition being analyzed; means formounting said chamber in said cell with both of said electrodes on thesame side of said chamber and with the outer face of said other wall incontact with said medium; and means for passing a selectively permeablefluid through said chamber between said walls.

9. In a measuring instrument for exposure to a constituent to bemeasured, the combination of: a first electrode having a polarographicsensitive electrode surface; means for defining an electrolyte spaceadjoining said sensitive surface, said means including a membranepermeable to the constituent to be measured, the outer surfaceofsaidmembrane being exposable to an environment containing the constituent; asecond electrode polarographically complementary tosaid first electrode,both said electrodes being positioned on the side of said membraneopposite the side exposed to said environment; and electrolyte meansproviding an ionic solution in said electrolyte space in contact withsaid sensitive surface and the inner surface of said membrane, andforming an ionic bridge between said first and second electrodes, thevolume of said electrolyte space being small to provide a shortequilibration time for said electrolyte means and a short time constantin the measurement.

10. In an instrument for measuring a constituent in either a gaseous orliquid environment, the combination of: a polarographic sensingelectrode; means definingan electrolyte space immediately adjacent tosaid sensing electrode, said means including a membrane permeable tosaid constituent, said membrane separating said electrolyte space fromsaid environment; a body of electrolyte with at least a portion of saidelectrolyte filling saidelectrolyte space; and a reference electrodeelectrically isolated from said sensing electrode except through saidelectrolyte and positioned on the same side of said membrane as saidsensing electrode for contact with said body of electrolyte, saidsensing electrode effecting a signal current through said electrolyteand said reference electrode by removal of said constituentf-romsaid-electrolyte space, said space being of small volume and providing ashort diffusion path between said membrane and said sensing electrodefor rapid equilibration of said current to changes of said constituentinsaid environment.

1-1. In a measuring instrument for use in determining the proportionalquantity of a nonionic dissolved gaseous component in a composition tobe analyzed, the combination of; an anode electrode and a cathodeelectrode; means for supporting said electrodes in predeterminedrelationship; chambermeans defining a chamber enclosing said electrodes,said chamber means including permeable membrane means for separatingsaid electrodes from the composition to'be analyzed, said membrane meansbeing permeable to said gaseous component and impermeable to interferingionic and nonvolatile components in the composition; an ionic solutionenclosed in said chamber for forming an ionic path between saidelectrodes; and means for impressing a predetermined electricalpotential across said electrodes to cause an ionic current flow in saidpath in response to transmission of said gaseous component from thecomposition-through said membrane means into said chamber.

12. In a measuring instrument for exposure-to a'coir stituent tobemeasured, the combination of: a first elec' trode having a sensitiveelectrode surface; a second electrode electrically isolated from saidfirst electrode; a membrane selectively permeable to said constituent;means 'for supporting said membrane for separating said electrodes fromsaid constituent with one face of said membrane closelyadjacent to saidelectrode surface to defines, liquid film space therebetween, the otherface of said membrane being exposable to an environment containing saidconstituent to be measured; and a body of electrolyte with at least aportion thereof positioned in said liquid film space in contact withsaid sensitive electrode surface and said membrane; for forming acurrent path from said second electrode through said electrolyte to saidfirst electrode.

13. In a polarographic measuring cell, the combination of: an anodeelectrode and a cathode electrode; means for supporting said electrodesin said cell in predetermined spaced relationship; a mediumelectrolytically bridging said electrodes to form an electrical circuittherewith; and selectively permeable barrier means car'- ried by saidcell for separating said electrodes and medium from a composition beinganalyzed, said barrier means permitting particular substances present insaid composition to pass therethrough and into said medium for producingchanges in electrical characteristics of said circuit.

14. In a polarographic cell, the combination of: an anode electrode anda cathode electrode; means for sup porting said electrodes in said cellin predetermined spaced relationship; and selectively permeable barriermeans carried by said cell and positioned with respect to saidelectrodes to define a space adapted for filling with a medium to forman electrical circuit between said electrodes, said barrier meansseparating both said electrodes from a composition being analyzedwhereby during cell operation particular substances present in saidcomposition will pass therethrough and into the medium for producingchanges in electrical characteristics of said circuit.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Busch et al.: Applications of the Dropping Mercury Electrodeto BOD Determinations, Tech. Info. Service, Oak Ridge, Tenn., May 27,1952; p. 3 and 21.

D. W. Brubaker and Karl Kammermeyer: Separation of Gases by PlasticMembranes, Industrial & Engineering Chemistry, vol. 46, No. 4, pp.733-742.

PatsntNo 2,913,386 November 1 1953 Mark T It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

ii' olmm 9,, 6, after "membrane" strike out semissiono Signed and this3rd day of May 196% Attest:

KARL v AL IJNE Commissioner of Patents

1. A POLAROGRAPHIC CELL FOR USE IN ANALYZING A COMPOSITION TO DETERMINETO QUANTITY OF A CERTAIN SUBSTANCE IN SAID COMPOSITION, SAID CELLCOMPRISING: AN ANODE AND A CATHODE; MEANS SUPPORTING SAID ANODE AND SAIDCATHODE IN FIXED SPACED RELATIONSHIP; MEANS FOR CONFINING AN ELECTROLYTEFORMING SUBSTANCE IN ELECTRICAL CURRENT CARRYING CONTACT WITH SAID ANODEAND SAID CATHODE; MEANS FOR IMPRSSING A PREDETERMINED ELECTRICALPOTENTIAL ACROSS SAID ANODE AND SAID CATHODE; BARRIER MEANS SURROUNDINGSAID ANODE AND SAID CATHODE AND SAID ELECTROLYTE FORMING SUBSTANCE TOPHYSICALLY SEPARATE AND ELECTRICALLY INSULATE SAID ELECTROLYTE FROM SAIDCOMPOSITION BEING ANALYZED, SAID BARRIER MEANS BEING PERMEABLE TO THESUBSTANCE IN SAID COMPOSITION THE QUANTITY OF WHICH IT IS DESIRED TODETERMINE, SAID SUBSTANCE BEING REACTABLE WITH SAID ELECTROYLYTE FORMINGSUBSTANCE TO ALTER THE ELECTRICAL CHARACTERISTICS OF SAID CELL, SAIDBARRIER MEANS BEING IMPERMEABLE TO ALL ELECTROLYTE FORMING SUBSTANCE;AND MEANS FOR OBSERVING BY RECTIONS BETWEEEN SAID ELECTROLYTE FORMINGSUBSTANCE AND SAID SUBSTANCE TO WHICH SAID BARRIER MEANS IS PERMEABLE.